What are the best practices for securing a Python web application against common security threats?

To protect your Python web applications, you should start with the basics - validate and sanitize all user inputs to protect against SQL injection and XSS attacks. You can make use of frameworks like Django or Flask, which come with built-in protection tools. You should also implement HTTPS to secure data in transit.

Remember to manage your sessions securely - you can think of your session tokens as the keys a hacker might look after, so they should be protected at all costs. Don't forget about securing your server and database as well - regular security audits are essential for identifying and rectifying any chinks in your applications before attackers can exploit them.